Shader "Custom/ImprovedPseudoShadow" {
    Properties {
        [Header(Base)]
        _MainTex ("Texture", 2D) = "white" {}
        _Color ("Main Color", Color) = (1,1,1,1)

        [Header(Shadow)]
        _ShadowColor ("Shadow Color", Color) = (0.2, 0.2, 0.3, 1) // 默认偏蓝的阴影
        _ShadowThreshold ("Shadow Threshold", Range(-1,1)) = 0.0
        _ShadowSmoothness ("Shadow Smoothness", Range(0,1)) = 0.1

        [Header(Lighting Mode)]
        _UseWorldLight ("Use Fixed World Light?", Range(0,1)) = 0
        _FakeLightDir ("Fake Light Dir (XYZ)", Vector) = (0.5, 1, 0.5, 0) // 模拟从右上方来的光
    }

    SubShader {
        Tags { "RenderType"="Transparent" }
        LOD 100

        Pass {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            // 开启 GPU Instancing 支持
            #pragma multi_compile_instancing
            #include "UnityCG.cginc"

            struct appdata {
                float4 vertex : POSITION;
                float3 normal : NORMAL;
                float2 uv : TEXCOORD0;
                UNITY_VERTEX_INPUT_INSTANCE_ID // Instancing ID
            };

            struct v2f {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
                float lightFactor : TEXCOORD1; // 传递光照因子
                UNITY_VERTEX_INPUT_INSTANCE_ID // Instancing ID
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            
            // 声明 Instancing 属性变量
            UNITY_INSTANCING_BUFFER_START(Props)
                UNITY_DEFINE_INSTANCED_PROP(fixed4, _Color)
                UNITY_DEFINE_INSTANCED_PROP(fixed4, _ShadowColor)
                UNITY_DEFINE_INSTANCED_PROP(float4, _FakeLightDir)
                UNITY_DEFINE_INSTANCED_PROP(float, _ShadowThreshold)
                UNITY_DEFINE_INSTANCED_PROP(float, _ShadowSmoothness)
                UNITY_DEFINE_INSTANCED_PROP(float, _UseWorldLight)
            UNITY_INSTANCING_BUFFER_END(Props)

            v2f vert (appdata v) {
                v2f o;
                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_TRANSFER_INSTANCE_ID(o, v);

                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);

                float3 normalWorld = UnityObjectToWorldNormal(v.normal);
                float3 lightDir;

                float useWorldLight = UNITY_ACCESS_INSTANCED_PROP(Props, _UseWorldLight);
                float3 fakeDir = normalize(UNITY_ACCESS_INSTANCED_PROP(Props, _FakeLightDir).xyz);
                float3 viewDir = normalize(WorldSpaceViewDir(v.vertex));
                // 用lerp实现分支
                lightDir = normalize(lerp(viewDir, fakeDir, useWorldLight));

                float dotProduct = dot(normalWorld, lightDir);
                o.lightFactor = dotProduct;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target {
                UNITY_SETUP_INSTANCE_ID(i);

                // 获取属性
                fixed4 mainColor = UNITY_ACCESS_INSTANCED_PROP(Props, _Color);
                fixed4 shadowColor = UNITY_ACCESS_INSTANCED_PROP(Props, _ShadowColor);
                float threshold = UNITY_ACCESS_INSTANCED_PROP(Props, _ShadowThreshold);
                float smoothness = UNITY_ACCESS_INSTANCED_PROP(Props, _ShadowSmoothness);

                fixed4 texCol = tex2D(_MainTex, i.uv) * mainColor;

                // 改进2：更平滑且可控的阈值计算 (Smoothstep)
                // lightFactor 越大说明越直接面对光源
                float lightIntensity = smoothstep(threshold, threshold + smoothness, i.lightFactor);

                // 改进3：基于光照强度的颜色插值 (Lerp)
                // 0 (背光) -> ShadowColor
                // 1 (受光) -> Texture Color
                fixed3 finalRGB = lerp(shadowColor.rgb * texCol.rgb, texCol.rgb, lightIntensity);

                return fixed4(finalRGB, texCol.a);
            }
            ENDCG
        }
    }
    FallBack "VertexLit"
}